The present invention relates to a semiconductor device equipped with a capacitor including a capacitor dielectric film made from a ferroelectric material or a high dielectric constant material and a method for fabricating the semiconductor device.
In accordance with recent development of digital technology, trend toward processing and storing massive data has been accelerated and electric equipment has attained higher performance. Therefore, semiconductor integrated circuit devices used in electronic equipment and semiconductor devices included in the semiconductor integrated circuit devices have rapidly been refined.
Accordingly, in order to increase the degree of integration of a semiconductor memory (a dynamic RAM), a technique to use a high dielectric constant film as a capacitor dielectric film instead of a conventional silicon oxide or silicon nitride film is now being widely studied and developed.
Also, in order to practically realize a nonvolatile RAM capable of more rapid write and read operations and a lower voltage operation than a conventional device, a technique to use, as a capacitor dielectric film, a ferroelectric film having a spontaneous polarization property is being earnestly studied.
In general, as materials for such a high dielectric constant film or a ferroelectric film, compounds having a bismuth-layer perovskite structure, such as barium strontium titanate, tantalum pentaoxide, lead zirconate titanate and bismuth strontium tantalum, are widely used.
Also, as a method for depositing a high dielectric constant film or a ferroelectric film, various methods including MOCVD (Metal Organic Chemical Vapor Deposition) are known. In any of these known methods, it is necessary to perform annealing in an oxygen atmosphere at a high temperature of approximately 600xc2x0 C. through 800xc2x0 C. after depositing a high dielectric constant film or a ferroelectric film, so as to crystallize the high dielectric constant film or the ferroelectric film.
On the other hand, as the memory cell structure of a DRAM or a nonvolatile RAM equipped with a capacitor including a high dielectric constant film or a ferroelectric film, a stacked memory cell structure has been proposed to meet the needs of a higher degree of integration of a semiconductor device. In the stacked memory cell structure, a transistor included in a memory cell is connected to a capacitor disposed above the transistor through a conducting contact plug. When the stacked memory cell structure is employed, the area of a memory cell can be reduced while keeping a large capacity necessary for storage, and hence, it is an indispensable structure for attaining a high degree of integration of a semiconductor device.
Now, a conventional semiconductor device having the stacked memory cell structure will be described with reference to FIG. 12.
As shown in FIG. 12, in the conventional semiconductor device, an isolation region 11 and a pair of impurity diffusion layers 12 working as source and drain regions are formed in surface portions of a semiconductor substrate 10. On the semiconductor substrate 10 between the pair of impurity diffusion layers 12, a gate electrode 14 is formed with a gate insulating film 13 sandwiched between the gate electrode 14 and the semiconductor substrate 10, and a sidewall 15 is formed on both sides of the gate insulating film 13 and the gate electrode 14. The pair of impurity diffusion layers 12, the gate insulating film 13 and the gate electrode 14 together form a transistor.
An interlayer insulating film 16 is formed so as to cover the transistor above the semiconductor substrate 10. On the interlayer insulating film 16, a first conducting barrier layer 18 having a function as an adhesion layer, a second conducting barrier layer 19 and a lower electrode 20 are successively formed, and an insulating film 21 of a silicon oxide film or a silicon nitride film is provided around the first conducting barrier layer 18, the second conducting barrier layer 19 and the lower electrode 20. On the lower electrode 20 and the insulating film 21, a capacitor dielectric film 22 and an upper electrode 23 are successively formed, and the lower electrode 20, the capacitor dielectric film 22 and the upper electrode 23 together form a capacitor.
A hydrogen barrier layer 24 having an insulating property is formed on the upper electrode 23 of the capacitor, and the first conducting barrier layer 18 and one of the pair of impurity diffusion layers 12 are electrically connected to each other through a conducting plug 25 formed in the interlayer insulating film 16.
The first conducting barrier layer 18 is formed in order to prevent a material for the conducting plug 25 from diffusing into the capacitor and thus lowering the adhesion in annealing performed in an oxygen atmosphere for crystallizing the capacitor dielectric film 22, and is made from a nitride material having a conducting property such as titanium nitride, tantalum nitride, titanium aluminum nitride or tantalum aluminum nitride.
The second conducting barrier layer 19 is formed in order to prevent contact resistance from increasing through oxidation of the first conducting barrier layer 18 or the conducting plug 25 by preventing oxygen from diffusing from above into the first conducting barrier layer 18 or the conducting plug 25, and is made from a single film of any of or a multilayer film including iridium, iridium oxide, ruthenium and ruthenium oxide.
The interlayer insulating film 16 is made of a silicon oxide film including boron or phosphorus (hereinafter referred to as a BPSG film).
The aforementioned conventional semiconductor device has, however, the following two disadvantages:
In the conventional semiconductor device, the first conducting barrier layer 18 having a function as an adhesion layer is provided between the interlayer insulting film 16 and the second conducting barrier layer 19. Therefore, adhesion between the first conducting barrier layer 18 and the second conducting barrier layer 19 can be secured, but adhesion between the first conducting barrier layer 18 and the interlayer insulating film 16 cannot be disadvantageously secured. Specifically, during the annealing performed at a high temperature in an oxygen atmosphere for crystallizing the capacitor dielectric film 22, the interlayer insulating film 16 and the first conducting barrier layer 18 can be easily peeled off from each other, and therefore, adhesion between the interlayer insulating film 16 and the capacitor cannot be secured. The reason will now be described with reference to FIGS. 13A and 13B.
As shown in FIG. 13A, the side face of the first conducting barrier layer 18 is not covered with the second conducting barrier layer 19. Therefore, when the annealing is performed at a temperature of 650xc2x0 C. through 800xc2x0 C. for crystallizing the capacitor dielectric film 22, oxygen of the atmosphere diffuses into the first conducting barrier layer 18, and hence, the first conducting barrier layer 18 is oxidized.
Since the first conducting barrier layer 18 has a characteristic to increase in its volume when oxidized, the thickness in a peripheral portion of the first conducting barrier layer 18 is increased as shown in FIG. 13B. Therefore, adhesion between the center portion of the first conducting barrier layer 18 and the conducting plug 25 is lowered, and hence, adhesion between the capacitor and the conducting plug 25 is lowered. As a result, there arises a problem that the contact resistance between the capacitor and the conducting plug 25 is increased.
The second disadvantage is that the hydrogen barrier layer 24 having an insulating property cannot completely block hydrogen. The hydrogen barrier layer 24 is deposited by CVD or sputtering, and any hydrogen barrier layer 24 obtained by any of these methods cannot completely block hydrogen.
When the hydrogen barrier layer 24 is deposited by the CVD, a gas used for the deposition occasionally includes SiH4 or H2, and hence, hydrogen is unavoidably excessively included in the atmosphere for depositing this layer. As a result, the atmosphere is unavoidably a reducing atmosphere. Accordingly, the capacitor dielectric film 22 is exposed to the hydrogen atmosphere, and the hydrogen of the atmosphere reduces the capacitor dielectric film 22. Therefore, oxygen deficiency is caused in the capacitor dielectric film 22, so as to cause degradation in the electric characteristic, such as large lowering of the remanence, of the capacitor dielectric film 22.
Alternatively, when the hydrogen barrier layer 24 is deposited by the sputtering in which hydrogen is not present in the resultant film, the resultant film is made from any of various oxides including Al2O3. Such a film has a characteristic that it cannot be a complete oxide, and hence, a grain boundary is formed in the film. Therefore, there arises a problem that, during annealing performed in a hydrogen atmosphere for recovering the transistor characteristic, hydrogen of the atmosphere passes through the grain boundary of the hydrogen barrier layer 24 to diffuse into the capacitor dielectric film 22.
In consideration of the aforementioned conventional problems, a first object of the invention is improving adhesion between a conducting plug formed in an interlayer insulating film and a capacitor formed on the interlayer insulating film, and a second object is, in annealing performed in a hydrogen atmosphere, definitely preventing hydrogen of the atmosphere from diffusing into a capacitor dielectric film.
In order to achieve the first object, the first semiconductor device of this invention includes an interlayer insulating film formed on a semiconductor substrate on which a transistor has been formed; an adhesion layer formed on the interlayer insulating film and made from a metal oxide not oriented; a capacitor composed of a lower electrode, a capacitor dielectric film made from a high dielectric constant material or a ferroelectric material and an upper electrode successively formed in this order on the adhesion layer; and a conducting plug formed in the interlayer insulating film and the adhesion layer for electrically connecting the transistor and the capacitor to each other.
In the first semiconductor device of this invention, since the adhesion layer made from the metal oxide not oriented is provided between the interlayer insulating film and the capacitor, adhesion between the interlayer insulating film and the capacitor is improved so that the contact resistance between the capacitor and the conducting plug can be lowered.
In the first semiconductor device, the adhesion layer is preferably amorphous.
Thus, the adhesion between the interlayer insulating film and the capacitor can be definitely improved.
In the first semiconductor device, the metal oxide of the adhesion layer preferably includes titanium aluminum oxide.
Thus, the adhesion between the interlayer insulating film and the capacitor can be definitely improved.
The first semiconductor device preferably further includes a conducting barrier layer formed between the adhesion layer and the conducting plug, and the lower electrode, and the conducting plug preferably connects the transistor and the conducting barrier layer to each other.
Thus, the adhesion layer suppresses volume increase of the conducting barrier layer, and hence, the interlayer insulating film and the conducting barrier layer are minimally peeled off from each other, so that the adhesion between the interlayer insulating film and the capacitor can be definitely improved.
In order to achieve the second object, the second semiconductor device of this invention includes an interlayer insulating film formed on a semiconductor substrate on which a transistor has been formed; a capacitor composed of a lower electrode, a capacitor dielectric film made from a high dielectric constant material or a ferroelectric material and an upper electrode successively formed in this order on the interlayer insulating film; a conducting plug formed in the interlayer insulating film for electrically connecting the transistor and the capacitor to each other; and an insulating upper barrier layer formed over the capacitor and made from a metal oxide not oriented.
In the second semiconductor device of this invention, when annealing is performed in a hydrogen atmosphere for recovering the transistor characteristic, hydrogen of the atmosphere minimally passes through the upper barrier layer. Therefore, the capacitor insulating film can be prevented from being degraded in its characteristic due to reduction with the hydrogen.
In the second semiconductor device, the upper barrier layer is preferably amorphous.
Thus, the hydrogen of the atmosphere can be definitely prevented from passing through the upper barrier layer.
In the second semiconductor device, the metal oxide of the upper barrier layer preferably includes titanium aluminum oxide.
Thus, the hydrogen of the atmosphere can be definitely prevented from passing through the upper barrier layer.
The second semiconductor device preferably further includes an insulating lower barrier layer formed between the interlayer insulating film and the lower electrode and made from a metal oxide not oriented.
Thus, when annealing is carried out in a hydrogen atmosphere for recovering the transistor characteristic, hydrogen of the atmosphere minimally passes through the lower barrier layer, and hence, the hydrogen can be prevented from diffusing into the interlayer insulating film and reaching the capacitor. Therefore, the capacitor dielectric film can be prevented from being degraded in its characteristic due to reduction with the hydrogen.
In the case where the second semiconductor device includes the lower barrier layer, the lower barrier layer is preferably amorphous.
Thus, the hydrogen of the atmosphere can be definitely prevented from passing through the lower barrier layer.
In the case where the second semiconductor device includes the lower barrier layer, the metal oxide of the lower barrier layer preferably includes titanium aluminum oxide.
Thus, the hydrogen of the atmosphere can be definitely prevented from passing through the lower barrier layer.
In the case where the second semiconductor device includes the lower barrier layer, the second semiconductor device preferably further includes a conducting barrier layer formed between the lower barrier layer and the conducting plug, and the lower electrode, and the conducting plug preferably connects the transistor and the conducting barrier layer to each other.
Thus, the lower barrier layer suppresses volume increase in the thickness direction of the conducting barrier layer, and hence, the interlayer insulating film and the conducting barrier layer are minimally peeled off from each other, so that the adhesion between the interlayer insulating film and the capacitor can be improved.
In the case where the second semiconductor device includes the lower barrier layer and the conducting barrier layer, the second semiconductor device preferably further includes an insulating side barrier layer formed over a side face of the conducting barrier layer and made from a metal oxide not oriented.
Thus, the side barrier layer suppresses the volume increase in the thickness direction of the conducting barrier layer, and hence, the interlayer insulating film and the conducting barrier layer are minimally peeled off from each other, so that the adhesion between the interlayer insulating film and the capacitor can be definitely improved.
In order to achieve the first object, the first method for fabricating a semiconductor device of this invention includes the steps of forming an interlayer insulating film on a semiconductor substrate on which a transistor has been formed; forming an adhesion layer on the interlayer insulating film from a metal oxide not oriented; forming, in the interlayer insulating film and the adhesion layer, a conducting plug having one end connected to the transistor; forming, on the adhesion layer, a capacitor electrically connected to the other end of the conducting plug and composed of a lower electrode, a capacitor dielectric film made from a high dielectric constant material or a ferroelectric material and an upper electrode successively disposed in this order on the adhesion layer; and performing annealing in an oxygen atmosphere for crystallizing the capacitor dielectric film.
In the first method for fabricating a semiconductor device of this invention, since the adhesion layer made from the metal oxide not oriented is formed between the interlayer insulating film and the capacitor, adhesion between the interlayer insulating film and the capacitor is improved, so that the contact resistance between the capacitor and the conducting plug can be lowered.
In the first method for fabricating a semiconductor device, the adhesion layer is preferably formed by sputtering carried out at a chamber pressure of 0.6 Pa or more and DC power of 12 kW or less.
Thus, the adhesion layer made from the metal oxide not oriented can be definitely formed between the interlayer insulating film and the capacitor.
In order to achieve the second object, the second method for fabricating a semiconductor device of this invention includes the steps of forming an interlayer insulating film on a semiconductor substrate on which a transistor has been formed; forming, in the interlayer insulating film, a conducting plug having one end connected to the transistor; forming, on the interlayer insulating film, a capacitor electrically connected to the other end of the conducting plug and composed of a lower electrode, a capacitor dielectric film made from a high dielectric constant material or a ferroelectric material and an upper electrode successively disposed in this order on the interlayer insulating film; forming an insulating upper barrier layer over the capacitor from a metal oxide not oriented; and performing annealing in a hydrogen atmosphere.
In the second method for fabricating a semiconductor device, when the annealing is performed in a hydrogen atmosphere for recovering the transistor characteristic, hydrogen of the atmosphere minimally passes through the upper barrier layer, so that the capacitor dielectric film can be prevented from being degraded in its characteristic due to reduction with the hydrogen.
In the second method for fabricating a semiconductor device, the upper barrier layer is preferably formed by sputtering carried out at a chamber pressure of 0.6 Pa or more and DC power of 12 kW or less.
Thus, the upper barrier layer made from the metal oxide not oriented can be definitely formed.
The second method for fabricating a semiconductor device of this invention preferably further includes, between the step of forming an interlayer insulating film and the step of forming a conducting plug, a step of forming an insulating lower barrier layer over a bottom face of the capacitor from a metal oxide not oriented, and the conducting plug is formed in the interlayer insulating film and the lower barrier layer in the step of forming a conducting plug.
Thus, when the annealing is carried out in a hydrogen atmosphere for recovering the transistor characteristic, the hydrogen of the atmosphere minimally passes through the lower barrier layer, and hence, the hydrogen can be prevented from diffusing into the interlayer insulating film and reaching the capacitor. Therefore, the capacitor dielectric film can be prevented from being degraded in its characteristic due to reduction with the hydrogen.
In the case where the second method for fabricating a semiconductor device includes the step of forming a lower barrier layer, the lower barrier layer is preferably formed by sputtering carried out at a chamber pressure of 0.6 Pa or more and DC power of 12 kW or less.
Thus, the lower barrier layer made from the metal oxide not oriented can be definitely formed.
In the case where the second method for fabricating a semiconductor device includes the step of forming a lower barrier layer, the second method preferably further includes, between the step of forming a conducting plug and the step of forming a capacitor, a step of forming a conducting barrier layer on the lower barrier layer and the conducting plug.
Thus, the lower barrier layer suppresses the volume increase in the thickness direction of the conducting barrier layer, and hence, the interlayer insulating film and the conducting barrier layer are minimally peeled off from each other, so that the adhesion between the interlayer insulating film and the capacitor can be improved.
In the case where the second method for fabricating a semiconductor device includes the steps of forming a lower barrier layer and a conducting barrier layer, the step of forming a capacitor preferably includes a sub-step of forming an insulating side barrier layer over a side face of the conducting barrier layer from a metal oxide not oriented.
Thus, the side barrier layer suppresses the volume increase in the thickness direction of the conducting barrier layer, and hence, the interlayer insulating film and the conducting barrier layer are minimally peeled off from each other, so that the adhesion between the interlayer insulating film and the capacitor can be definitely improved.